Electrical equipment, as well as the primary feed circuits to which the electrical equipment is connected, is protected against excessively high fault currents by use of current limiting fuses. One type of such fuse is housed within a fuse holder designed specially for electrical equipment such as transformers and primary switch/fuse modules serving pad mounted and underground service applications. This type of fuse holder is an externally operated design which accommodates the small space typically available with pad mounted and underground equipment. The current limiting fuses often used with these fuse holders are very sensitive to oil and moisture leaks. Fuse holders are subjected to hot transformer oil immersion within the transformer or switch and to ambient weather conditions outside the transformer or switch. A fuse holder which does not provide good hermetic seals can cause the top closure or cap of the fuse holder to be expulsed quite rapidly due to the creation of gases within the fuse holder when the fuse operates.
Conventional fuse holders include wet wound type fuse holders, such as those made by Kuhlman Electric Corporation of Versailles, Kentucky and by the General Electric Company of Hickory, N.C. Construction of these fuse holders include a first contact at the distal or inner end of the fuse holder, a second contact spaced axially along the length of the fuse holder and a mounting flange at the proximal or outer end of the fuse holder. The main body of the tube is made by wet winding resin-impregnated fibers around a mandrel, the electrical contacts and the mounting flange.
Another type of fuse holder uses a preformed composite tube to which the mounting flange and electrical contacts are mounted. One such fuse holder is made by Cooper Power Systems of Pittsburgh, Pa. This fuse holder has the first electrical terminal threadably mounted to the distal end of the tube and the mounting flange threadably mounted to the proximal end of the tube. The second electrical contact is centrally located along the tube and is of a split-ring design which can partially collapse on itself. The second electrical contact has an outwardly extending boss which passes through an opening in the tube. Once the boss is properly positioned, the split ring expands to its full circular shape to serve as the second electrical terminal within the tube.